This invention relates generally to systems and methods for monitoring the vertical level (height) of fluid contained in a container. More particularly, the invention concerns differential pressure level monitoring systems and methods.
Various systems and methods exist for monitoring the vertical level of fluid in a container. As used herein, a container generally refers to a structure for holding or transporting a fluid, such as a reservoir, an open or closed channel, a tank, or a reactor. These include visual measurement systems, microwave technologies, ultrasonic technologies, submerged pressure transducers, and differential pressure bubbler systems. Each of these includes various drawbacks. Visual measurement systems are not efficient. Ultrasonic technologies, microwave technologies, and submerged pressure transducer systems are expensive and they do not work well with turbulent processes, with fluids containing foam and/or suspended solids, or with corrosive fluids.
Existing differential pressure bubbler systems work well for measuring the vertical level of fluid in situations where turbulence, debris, foam, or corrosive substances make other systems impractical. However, conventional differential pressure bubbler systems suffer from a number of problems. For instance, they tend to become clogged often, which affects the accuracy of pressure measurements or prevents these measurements entirely. Further, they need frequent cleaning to remove build-up or clear clogs.
As an example, FIG. 1 shows a typical differential pressure bubbler system 10. As shown, bubbler system 10 includes a tank 12 containing fluid 14, a small-diameter bubble tube 16, an air supply 18, and a differential pressure controller 20. In general, bubbler system 10 measures the hydrostatic pressure in fluid 14 near the bottom of tank 12 by comparing atmospheric pressure with the pressure required to force air from bubble tube 16. Bubble tube 16 is a small-diameter (less than 1.0 inch diameter) vertical tube about 15 feet long, which permits bubbles to flow from its opening 141 near the bottom of tank 12. Air supply 18 provides air to bubble tube 16 at a pressure slightly greater than the hydrostatic pressure at the end 22 of bubble tube 16. Small-diameter tubing is used for bubble tube 16 to reduce false readings and lag time in reading pressure changes, which can occur when a large volume of air is maintained in pressure tube 16. Differential pressure controller 20 is connected to bubble tube 16 and includes one or more pressure sensors that sense atmospheric pressure and the air pressure in bubble tube 16.
Differential pressure controller 20 calculates hydrostatic pressure, H, at the opening 22 of bubble tube 16 by comparing the atmospheric pressure and bubble tube pressure according to the following formula: H=xcex94P/Sg, where xcex94P=the difference between bubble tube pressure and atmospheric pressure, and Sg=specific gravity of fluid 14. The vertical level of fluid 14 above the opening can be determined based on the hydrostatic pressure, H, at the opening 22 of bubble tube 16. Further, if the vertical level of fluid 14 is known, the same system can be used to determine the specific gravity, Sg, of fluid 14.
Such conventional differential pressure bubbler systems suffer from a number of problems. For example, bubble tube 16 periodically becomes clogged with build-up, scale, sludge, settlement and/or debris, which affects the accuracy of pressure measurements or prevents these measurements entirely. As such, bubble tube 16 often needs to be purged with high-pressure air to clear obstructions. Purging, however, does not completely remove scale or other build-up on the surfaces of bubble tube 16 and at opening 22. Thus, bubble tube 16 is periodically removed from tank 12 to clean scale and other materials from the bubble tube 16. Removing bubble tube 16 for cleaning is expensive and time-consuming. Further, such periodic removal and cleaning can be dangerous, depending on the type of fluid 14 in tank 12.
Accordingly, there is a need for improved systems and methods for measuring the vertical level of fluid in a container. Further, a need exists for improved low-maintenance differential pressure bubbler systems and methods.
In order to overcome the above-described problems and other problems that will become apparent when reading this specification, aspects of the present invention provide a method for measuring the vertical level (height) of fluid in a container. According to one aspect of the invention, a method for measuring the vertical level of fluid in a container includes moving air downward along the inside of a bubble tube at an angle of about 5 degrees to about 85 degrees from vertical into the fluid. According to another aspect, the method includes injecting a mixture of air and steam into fluid in a container via a bubble tube.
Aspects of the present invention further provide a differential pressure bubble tube system that includes a bubble tube mounted to a container at an angle of about 5 degrees to about 90 degrees. Aspects additionally provide a bubble tube having a diameter of about 1 inch to about 6 inches. Further aspects include a bubble tube having pressurized air and steam inputs. Other features and advantages of various aspects of the invention will become apparent with reference to the following detailed description and figures.